The Caspian Seal belongs to the Phocina group of northern seals, which includes the Ringed Seals (Pusa), the Harbour and Spotted Seals (Phoca), and the Grey Seal (Halichoerus). The radiation of the Phocina group is now believed to have started in the northern seas of the late Pliocene, 2-3 million years ago, and was accompanied by invasion of the continental basins, though the paleogeography in this period is not clear (Palo and Väinöla 2006, Fulton and Strobeck 2010).

The taxonomic relationships between the seals of the continental lakes and open ocean has long been contentious, and the placement of the Caspian Seal has varied between the genera Pusa and Phoca. Cladistic and phylogenetic studies from the 1970s to present based on morphology, and more recently mitochondrial and nuclear gene DNA sequence datasets, considered Phoca, Pusa, Histriophoca, and Pagophilus to be a monophyletic group (Wozencraft 2005). These analyses support two clades, Pagophilus and Histriophoca and the Phocina group, Phoca, Pusa, and Halichoerus (Rice 1998, Bininda-Emonds et al. 2007, Arnason et al. 2006, Fulton and Strobeck 2010, Nakatuya and Bininda-Emonds 2012) but the placement of Halichoreus within the group has been problematic.

Using a multigene mitochondrial dataset, Palo and Väinöla (2006) considered Pusa not to be a monophyletic group, with the Phocina forming a polytomy, but suggested that the Caspian Seal was most closely related to Halichoerus. Similarly, Arnason et al. (2006), using whole mitochondrial genome sequences also concluded the Caspian Seal to be most closely related to the Grey Seal, with the Baikal Seal forming a sister taxon, with Phoca and Ringed Seals outside this group. Fulton and Strobeck (2010) using nearly 9,000 base pairs of nuclear gene sequences and complete mtDNA genomes, placed Halichoreus basal to the group, with Pusa and Phoca as sister clades, and Pusa caspica basal to the Pusa genus. The most recent assessment (Nyakatura and Bininda-Emonds 2012), a super tree analysis of all carnivora combining 114 trees from the literature and 45,000 base pairs of DNA sequence, supports the grouping of Halichoreus within Pusa, with Phoca as a sister clade. Pusa caspica and Halichoreus grypus are indicated as sister species, diverging about 1.6 million years ago. Nyakatura and Bininda-Emonds (2012) advocate subsuming Halichoreus and Pusa within the Phoca genus.

Due to a decline exceeding 70% over the last three generations (18.8 years; Pacifici et al. 2013), reduction in the number of sites used (range reduction within the overall geographic range), current by-catch and hunting levels that almost certainly exceed sustainable removal levels, and the multiple ongoing negative impacts on the habitat of the Caspian Seal, this species is classified as Endangered under criterion A2b.

Caspian Seals are confined to the Caspian Sea. They range throughout the sea with seasonal migration between the southern, middle, and northern basins. More than 99.9% of breeding takes place on ice, which covers the shallow northern parts of the Caspian Sea in from late December to early April in typical years (Krylov 1990, Dmitrieva 2013, Dmitrieva et al. 2015a). Occasional observations have been made of low numbers (a few tens of individuals) breeding on islets off Turkmenistan (Krylov 1990, Dmitrieva 2013).

Historically, the population of Caspian Seals was estimated to have exceeded one million (Krylov 1990, Härkönen et al. 2012). The most recent estimates of abundance are based on aerial surveys of the breeding population on the northern ice field conducted annually in February between 2005 and 2012 (Härkönen et al. 2008, Dmitrieva et al. 2015b). During this period estimated annual pup production ranged between 8,200 (95% confidence intervals 7,130-9,342) and 34,000 (95% confidence intervals 31,275-36,814). This would suggest there are currently approximately 68,000 reproductively mature individuals (male and female, based on the greatest observed pup production), with the total population in the region of 104,000 to 168,000 individuals derived from an age structured model (Härkönen et al. 2008, 2012; Dmitrieva et al. 2015b). Variation in weather conditions during surveys may account for some of difference in pup counts between years, but additional contributions from biological factors affecting fecundity cannot be excluded at this time (Dmitrieva et al. 2015b). The variability in annual pup makes the current population trend uncertain, and a longer time series is necessary to directly assess the demographic trajectory (Dmitrieva et al. 2015b). However, if pup mortality exceeds 50% due to a combination of natural and anthropogenic causes (a realistic scenario), this could be sufficient to result in ongoing declines (Härkönen et al. 2012).

The population decline throughout the 20th century has been reconstructed by a demographic model using hunting statistics. By the 1950s–1960s, the population was estimated from this model to have been reduced to between 400,000-500,000 Seals (Härkönen et al. 2012), while an estimate based on a harvest of 86,000 pups in 1966, believed to be most pups born that year, also produced an estimate of 500,000 Seals for that year (Krylov 1990). Aerial surveys conducted in 1976 and 1980 suggested an estimate of 450,000 animals (Krylov 1990), although the hind-casting analysis suggests a population of only about 200,000 Seals remaining at that time (Härkönen et al. 2012). Surveys in 1987 and 1989 resulted in an estimate of approximately 360,000-400,000 (Krylov 1990), but again the hind-casting analysis suggests this might again have been an over-estimate, with perhaps only about 130,000 Seals remaining by the late 1980s. Overall, the hind-casting analysis indicated a population reduction of about 66% during 1867-1964 and a further reduction of 73% during 1965-2005 (Härkönen et al. 2012).

Härkönen et al. (2012) estimated the total population of adult females as 354,210 in 1945 and 21,000 in 2005, later revised to 34,000 by Dmitrieva et al. (2015b) after accounting for survey observation errors. Although pup production has been revised upwards in more recent publications, this would not affect the relative decline, since it would imply correspondingly higher historical population sizes. The IUCN Criterion A calculator was used to project declines over a three generation period 1955-2015, indicating adult female numbers declined 91.5%. However, the scale of decline is dependent on estimated values for parameters such as pup survival and fertility rates, about which there is some uncertainty (Härkönen et al. 2012). Therefore a more conservative position for the purposes of IUCN classification would be to accept a relative decline of at least 70% until more data are available to refine the historical demography.

Caspian Seals are a small bodied, ice-breeding species, with little sexual dimorphism. Average body length reaches 126-129 cm, with a maximum body length of approximately 140 cm (Wilson et al. 2014). Both sexes become sexually mature at about 6 years of age, with most breeding females (74% in a 1974 sample) aged between 8 and 17 years (Popov 1979, 1982). The pregnancy rate for females older than 9 is reported to be as low as 0.2-0.33 (Watanabe et al. 1999, Miyazaki 2002), and Krylov (1990) reports a similar low rate of 0.34 for females aged 10-14 years. Härkönen et al. (2012), acknowledge that the reproductive rate is low in females >20 years old, but suggest that the reproductive rate is >0.5 for females <20 years old taken together as a group. Since females <20 years old make up approximately two-thirds of the population of adult females, they probably drive the overall reproductive rate for the population up to about 0.5. Both Watanabe et al. (1999) and Härkönen et al. (2012) attribute the lower reproductive rates of older females to the effect of long term exposure to organochlorine contaminants in the older animals. Accumulation of contaminants with age has been documented in Caspian seals, but most animals appear to be below thresholds associated with reproductive pathologies (Wilson et al. 2014).

Pups are generally born from mid-January to late February on the ice, with a birth weight of around 5 kg (Popov 1979), and are nursed for 4-5 weeks. In contrast to ringed seals, females do not usually construct lairs (Frost and Lowry 1981), possibly because sufficient amounts of snow overlying the ice are normally lacking. Pupping on the ice without lairs has allowed direct counts of pups to be made in the recent aerial surveys (Härkönen et al. 2008, Dmitrieva et al. 2015). Pups do not enter the water until the ice melts in mid to late March.

The first documented observations of small numbers of Seals breeding in other parts of the Caspian were made in 1982, with females reported pupping on small sand islands in the southern part of the Caspian Sea, although it is likely this behaviour was not new (Krylov 1990). Large numbers of mostly nonbreeding Seals spend the winter in the middle and southern Caspian, with one estimate of 15,000 Seals along the Turkmenistan coast (Krylov 1990).

A post-breeding moult occurs from April to early May, during which the Seals first use the ice and then islands, sand bars, and reed beds for hauling out (Badamshin 1970, Krylov 1990). Presently, Komsomolets Bay and the Durnev Islands in Kazakhstan and Malyj Zhemchuzhnyj island in Russian waters represent the most important moulting habitats (Dmitrieva 2013). Aggregations of several tens of thousands of individuals can be found in Komsomoletz Bay during this period, and around ten thousand at Malyj Zhemchuzhnyj.

During late spring, summer, and early autumn, Caspian Seals are distributed throughout the Caspian Sea. They feed throughout the region, exploiting both the shallow basin in the north and the deep middle and southern basins (Krylov 1990). Recent satellite telemetry studies indicate about 60% of animals move to the middle and southern Caspian, with the remainder staying in the north, primarily around the inflow of Volga and Ural rivers (Dmitrieva 2013). The telemetry studies suggest considerable individual variation in summer migratory and foraging behavior, with individuals spending the summer period separated among shallow, intermediate, and deep water locations. This may reflect individual specialization or niche partitioning in relation to habitat or prey types (Dmitrieva et al. 2015a).

During the post-moult summer period Seals rarely haul out, spending several months at sea feeding. In late autumn the breeding adults gather in the northeast, hauling out on sandy islands and reed beds in increasing numbers until ice begins to form (Krylov 1990). When the surface freezes over, females form aggregations on the ice to give birth to their pups, tending to gather along cracks in the ice giving them ready access to the water, although like Ringed Seals they also construct and maintain holes in the ice for water access (Heptner et al. 1996, Härkönen et al. 2008).

Diving capacity for Caspian Seals is comparable to other small phocids, with maximum dive depths exceeding 200 m and dive times exceeding 20 minutes, but most dives are typically shallower than 15 m and shorter than 5 minutes. During the summer foraging areas are not limited by proximity to haul out sites, and animals may spend up to six months at sea. Foraging appears to be primarily benthic (Dmitrieva 2013).

Caspian Seals feed on a variety of fish species. During the summer and autumn, Seals move to and congregate where prey are abundant, particularly Caspian Kilka (Clupeonella sp.), Caspian Silverside (Atherina mochon), and Caspian Gobies (Gobidae) (Krylov 1990), with Clupeonella species historically making up a major proportion of their total annual diet (Kosarev and Yablonskaya 1994). A report on fish found in the stomachs of Seals in the northern Caspian in 1986-1987 (Piletskii and Krylov 1990) suggested that fish eaten in order of frequency were Roach (Rutilus rutilus), Zander (Lucioperca lucioperca), Gobies (Knipowitschia sp., Neogobius kessleri and Benthophilus sp.), and Bream (Blicca bjoerkna and Abramis brama), followed by C. deliculata and other species. A preliminary study from faecal samples collected on the Apsheron Peninsula in June 2001 and March 2002 suggested that Gobies, Silverside, and shrimp were important constituents of the diet of Seals at those times (Eybatov et al. 2002). New studies of diet in Caspian Seals are required in order to get an accurate picture of current prey in different areas of the Caspian in light of potential changes to the abundance of fish species due to recent ecological changes occurring in the region.

Caspian Seals have been commercially exploited since the late 18th century. Harvests averaged 119,000-174,000 per year throughout the 19th century, with peaks of 300,000 having been recorded. In the 20th century, harvest levels peaked in the 1930s with an average annual harvest of 164,000 and a maximum single year take of 227,600. The numbers of Seals taken fell during World War II to an average of 60,800 per year, and subsequently ranged between a low of 41,400 and a high of 108,300 for the period 1951-1975 (Krylov 1990, Härkönen et al. 2012). Commercial harvesting was temporarily halted in 1996 after a much-reduced estimated take of 14,000 Seals. Since the start of the 21st century smaller scale commercial and scientific hunting has taken place in Russia, typically with recorded hunts of tens or hundreds of individuals per year, with a maximum of 4,600 (in 2003-2004), reported for the period up to 2010. Official hunting is conducted under a quota system administered by an inter-governmental body, the Caspian Bioresources Commission. Typical annual quotas are for 18,000 Seals, with 8,000 allocated to Russia, and the remainder divided among the other Caspian states. The scientific rationale for the quotas is not clear. Currently only Russia actively pursues official hunting under the quota, but large scale hunting does not appear to be commercially viable at present and recorded takes are far below the official quota levels (Härkönen et al. 2012, Dmitrieva et al. 2013). The level of ‘unofficial’ or illegal hunting is poorly documented, but illegal hunting on ice on the scale of hundreds of Seals is known to take place periodically (Dmitrieva et al. 2013). Seal skins are used for hats and other clothing in Russia, while Seal blubber is used as a medicinal tonic, fishing bait, and cattle feed in Kazakhstan and Turkmenistan. The total economic value and trading networks for Seal products remain to be fully determined, but high quality individual seal skins may sell for up to $100 US dollars at the point of origin, while seal oil can sell for $14.00 per litre in local markets (Dmitrieva et al. 2013).

Unsustainable hunting was the main driver of Caspian Seal decline during the 20th century (Härkönen et al. 2012), and human caused mortality continues to be the main ongoing threat to the population. Recently, by-catch of Seals, primarily in illegal Sturgeon fisheries has been identified as a major cause of Seal mortality (Dmitrieva et al. 2013). Based on semi-structured interviews conducted in fishing communities from Dagestan (Russia), Astrakhan region (Russia), and Atyrau region (Kazakhstan), Dmitrieva et al. (2013) documented a minimum by-catch of 1,215 Seals during the 2008-2009 fishing season, 93% of which occurred in illegal Sturgeon fisheries. However, the study sampling reflected less than 10% of the overall poaching activity in the north Caspian, so the actual by-catch is likely to be substantially higher, and to exceed the Potential Biological Removal level (Wade et al. 1998) for the population (Dmitrieva et al. 2013). Moreover, the survey did not cover fisheries in the middle and southern Caspian. Iranian commercial fisheries cause an estimated mortality of 500 Seals annually (Eybatov et al. 2002). Further work is needed to fully quantify Seal by-catch rates throughout the Caspian Sea, and its implications for population demography. Fishermen frequently sell skins and blubber from bycaught Seals.

Natural sources of mortality include predation and disease. The primary non-human predators are Wolves (Canis lupus) and Sea Eagles (Haliaeetus spp.). Krylov (1990) estimated that Wolves killed 17-40% of Caspian Seal pups on “some breeding grounds from 1974 to 1976”, while Eagles took less than 1% of pups. The reverse was found during recent aerial surveys (Harkonen et al. 2008, Dmitrieva et al. 2015b). Few Wolves were observed each year between 2005-2012, but up to 3,100 Eagles. Eagles are likely to primarily scavenge afterbirth and dead pups, but may also be capable of killing unaccompanied unweaned pups.

Mass mortality events occurred in 1997 and 2000-2001, killing several thousand Seals each time, and have since been attributed to canine distemper virus (CDV). Presence of a hitherto unknown strain of CDV was confirmed in one dead Seal in 1997 (Forsyth et al. 1998), and the same strain was confirmed as the primary cause of death in Seals dying in 2000 in Kazakhstan and Azerbaijan (Kennedy et al. 2000, Kuiken et al. 2006). Examination of archived stranding records in Azerbaijan since 1971, show an increased mortality every few years, suggesting the possibility of previous outbreaks of CDV (Wilson et al. 2014). A serology study of archived samples indicated that CDV was present in Caspian Seals in 1993, 1997, and 1998 (Ohashi et al. 2001). There have been no further mass mortalities since 2001, but disease would become a concern should they reoccur.

Degradation of the Caspian Sea ecosystem and overexploitation of primary food resources may also be threats to Caspian Seals (Reijnders et al. 1993, Barannik et al. 2004). An invasive of Comb Jellyfish, Mnemiopsis leidyi, arrived in the Caspian Sea via ship ballast water in the Volga-Don Canal in 1999 (Ivanov et al. 2000). Comb Jellyfish consume zooplankton rapidly, leading indirectly to a reduction in fish stocks and a substantial impact on local fisheries. A 70% reduction in commercial landings of three species of Kilka was recorded within three years of the Comb Jellyfish invasion (Kideys et al. 2005). Kilka are thought to be important prey for Caspian Seals in the central and southern parts of the sea, and the invasion of Comb Jellyfish is considered a threat to the Seals (Ivanov et al. 2000, Eybatov et al. 2002). In addition to impacts from Comb Jellyfish, most commercial fisheries in the Caspian are considered to be severely depleted or extinct due to unsustainable fishing practices and/or loss of fish habitats such as spawning grounds (Strukova and Guchgeldiyev 2010). While Caspian Seals are known to feed to on commercially important fish species, commercial catch rates are not necessarily an indicator of prey availability, and Seals have a varied and adaptable diet which includes non-commercial species such as Gobies. To date is has not been possible to make any quantitative assessment on potential impacts from changes in Caspian food webs and Caspian Seal energetics and demography. Dmitrieva et al. (2015) did not find a significant correlation when testing for association between annual pup production and net primary productivity 2005-2012, but a longer time series of surveys is required to achieve adequate statistical power.

The Caspian Sea has no outlet and receives most of its input from the Volga, Ural, and other rivers. Contamination of the Volga with lead, copper, zinc, and cadmium has increased dramatically since the mid-1980s, but levels in Seals do not appear to be elevated, with the exception of zinc in some diseased animals that may have suffered homeostatic disturbance of trace metal levels (Anan et al. 2002).

Organochlorine levels (principally polycholorinated biphenyls (PCBs) and dichlorodiphenyltricholoethanes (DDTs)) have been assessed for Caspian Seals dying in the 1997-2001 CDV epizootics (Hall et al. 1999; Kajiwara et al. 2002, 2008; Wilson et al. 2014). Most animals were found to have levels below thresholds believed to cause toxic effects in mammals. Overall levels in Caspian Seals were lower than those seen in European Seal species, comparable to Baikal Seals, and higher than those reported for Arctic species (Wilson et al. 2014). Presently there is no evidence that organochlorine burdens in Caspian Seals cause reproductive or immune impairment, or contributed to the 1997-2001 CDV outbreaks at a population level, although some individual Seals may have high burdens (Kuiken et al. 2006, Eybatov et al. 2002, Härkönen et al. 2012, Wilson et al. 2014). Organochlorine accumulation was found to be primarily age related, which means animals at the older end of the age distribution may be at risk of crossing toxicity thresholds towards the end of their reproductive lifespan (Wilson et al. 2014). It has been recommended that levels of persistent organic pollutants should be monitored in the future due to the continuing industrial development around the Caspian region and time elapsed since the last survey following the CDV epizootics (Wilson et al. 2014).

Combined juvenile mortality from continued hunting, natural predation, and fisheries by-catch is believed to be unsustainable. Overall mortality before breeding from all sources is likely to be in the region of 50% (Härkönen et al. 2008). Demographic models indicate such a high rate of juvenile mortality would be capable of causing a continuing decline in the Caspian Seal population, with lowered fertility due to organochlorine contamination being a relatively minor factor (Härkönen et al. 2012). Variation in annual pup production determined from aerial surveys makes empirical estimation of current population trends uncertain (Dmitrieva et al. 2015b), and a longer time series is necessary to assess the demographic trajectory directly.

As a landlocked ice-breeding species with no option to migrate to alternative habitats, Caspian Seals may be vulnerable to future climate change (Kovacs et al. 2012). Warming may cause a reduction in the spatial extent, temporal duration, and stability of the winter ice breeding habitat. Premature break-up of the ice sheet before pups are moulted will cause significant mortality among pups of the year. January-March 2007 was one of the mildest winters in the Caspian in recent years, with ice cover suitable for breeding limited to a narrow strip along the coastline of the north-east Caspian. Storms in mid-February may have caused ice-flows with large numbers of pups to be swept out to sea, and pup counts for that year were less than one third the maximum observed for 2005-2012 (Dmitrieva et al. 2015b). It has also been suggested that poor ice conditions may play a role in the epidemiology of CDV outbreaks due to Seal crowding on limited haulout space and poor condition of weaned pups (Kuiken et al. 2006). Long term trends in Caspian Sea ice cover and the implications for population demography remain to be fully assessed.

Through the geological history of the Caspian, there have been several substantial fluctuations of sea level (Dumont 1998), which will have affected the relative amounts of shallow and deep water habitats available to Seals. The population adapted to those past changes, but there is some concern about whether the same will be possible for future sea level changes given added pressures of habitat loss and human impacts.

Further threats to the Seals on shore and on ice now come from increasing disturbance due to offshore and shoreline developments. One of the largest oil fields in the world is currently being developed in the Caspian, with the construction of numerous offshore oil drilling islands, pipelines, shipping access to these, and onshore logistics facilities. A recent study found that breeding Seals are using shipping channels as artificial leads into the ice and are giving birth close to the edge of these channels. A significant proportion of the breeding population and pups may therefore experience disturbance by shipping traffic depending on the ice conditions (Härkönen et al. 2008). More research is required to quantify the likely impacts of this intensive oil development. The coasts of Kazakhstan, Azerbaijan and Iran have also seen increased development for domestic and leisure use in recent years, with many previously undisturbed stretches of coast now being developed.

Disturbance of island and reef haulout sites by illegal fishing activities and opportunistic Seal hunting are another ongoing problem. Recent surveys have found that the Caspian Seal has effectively disappeared from Azerbaijan, with the once important haulout sites of the Apsheron Peninsula and Archipelago abandoned. These sites were used by many thousands of Seals until the 1930s when they were heavily hunted (Krylov 1990). However, between 1997 and 2002 a few hundred Seals were still counted regularly at these sites (e.g., Allchin et al. 1997, Wilson et al. 2014). Few live Seals have been seen in this area since 2004 (Wilson et al. 2014). The overall Caspian Seal population decline since 2002 is unlikely to account for this total disappearance, which is most probably due in part to severe disturbance by illegal fishing and other coastal activities (T. Eybatov, unpublished data). Similar declines in the regularity of Seal occupancy have also been noted recently at other sites, such as South West Island near the Ural Delta and Osushnoy Island (Kazakhstan), Bautino (Kazakhstan), and in Turkmenbashi Bay (Turkmenistan). The number of Seals at Ogurchinsky Island (Turkmenistan) has also declined from several thousand in the 1980s to a few hundred (P. Erokhin, unpublished observations). The only previously recorded haulout site in Iran, at Ashoora Island, is no longer used by Seals (H. Asadi pers. comm.). There is a need to develop an inventory of all haulout sites throughout the Caspian together with archived and current records of Seal occupancy (Wilson and Goodman 2012).

Various prohibitions, quotas, and protective measures have been taken to conserve the Caspian Seal, beginning in 1940 when seal nets were prohibited. The harvest of moulting Seals in the spring was ended in 1946, and in 1952 the Apsheron Archipelago in Azerbaijan was closed to sealing. Female harvesting on the breeding grounds was stopped in 1966 and all take was prohibited on the eastern islands of the northern Caspian in 1967. These last two changes led to a complete change in the commercial harvest, resulting in a switch to newborn and moulted pups. Quotas on harvest of pups, purportedly based on biological data, began in 1970 (Krylov 1990), although in retrospect the quotas were at unsustainable levels. The Russian Federation continues to consider the Caspian Seal to be a ‘harvested’ species, with quotas set through the Caspian Bioresources Commission (Härkönen et al. 2008, 2012).

A Seal Conservation Action and Management Plan was approved by the nations bordering the Caspian Sea, pursuant to the 2003 Framework Convention for the Protection of the Marine Environment of the Caspian Sea (Caspian Environment Programme 2007), but it had no legally binding actions. The action plan recommended cessation of hunting, measures to reduce by-catch in legal and illegal fisheries, and the strategic creation of protected areas of sea, ice, and shore. However, to date none of the Caspian states have taken steps to implement the action plan. In 2012 the CaspEco Project, a UNDP funded follow up to the Caspian Environment Programme, published a framework report and road map for the establishment of a network of protected areas for Caspian Seals, including suitable locations (Wilson and Goodman 2012), but no further action has yet taken place. A number of small non-governmental organizations within Caspian countries are involved in producing educational materials and promoting awareness of Caspian Seals. In Iran, localised work with fishing communities has been conducted promoting release rather than killing of live animals found entangled in fishing gear, and a stranded seal rehabilitation facility has been established. In 2014 the Caspian States banned all catching of wild Sturgeon and in recent years Kazakhstan has increased maritime patrols to counter Sturgeon poaching which in principle may have potential to also help reduce seal by-catch.